The Xe Bang Fai River cave is crowded with outsize features, such as this large limestone drapery formation.

First traversed on a bamboo raft by a French explorer in 1905, the cave, known locally as Tham Khoun Xe and occasionally visited by tourists, went unstudied for 90 years as war and political turmoil in Laos kept researchers out of the Southeast Asian country.

A French team returned briefly in 1995, but little useful data was gleaned. Caver John Pollack staged his first expedition to the site in 2006.